El Gran Terremoto de Valdivia (The Great Earthquake of Valdivia)

Date	22 May 1960 (1960-05-22)
Magnitude	9.5 Mw[1]
Depth	33 km
Epicenter location	Cañete
Countries/ regions affected	Chile
Casualties	2231, 3000, 5700[2] or 6000[3]

The 1960 Valdivia earthquake or Great Chilean Earthquake (Spanish: Gran terremoto de Valdivia) of 22 May 1960 is to date the most powerful earthquake ever recorded, rating 9.5 ^[1] on the moment magnitude scale. It occurred in the afternoon (19:11 GMT, 14:11 local time) and its resulting tsunami affected southern Chile, Hawaii, Japan, the Philippines, eastern New Zealand, south east Australia and the Aleutian Islands in Alaska.

The epicenter was near Cañete (see map) some 900 km (435 miles) south of Santiago, although Valdivia, Chile was the most affected city. It caused localised tsunamis that severely battered the Chilean coast, with waves up to 25 metres (82 ft). The main tsunami raced across the Pacific Ocean and devastated Hilo, Hawaii. Waves as high as 10.7 metres (35 ft) were recorded 10,000 kilometres (6,000 miles) from the epicentre, and as far away as Japan and the Philippines. The death toll and monetary losses arising from such a widespread disaster can never be precisely known. Various estimates of the total number of fatalities from the earthquake and tsunamis have been published, with the USGS citing studies with figures of 2231, 3000, or 5700 killed,^[2] and another source uses an estimate of 6000 dead.^[3] Different sources have estimated the monetary cost ranged from 400 million to 800 million US dollars^[2] (or 2.8 to 5.5 billion in 2007 dollars, adjusted for inflation.)

[edit] Earthquake development

Global seismic release from 1906 to 2005, the graph shows that almost 25% of the energy was concentrated in the Great Chilean Earthquake alone.

A Valdivia street after the earthquake of 22 May 1960

The town of Riñihue flooded during the Riñihuazo.

The Great Chilean Earthquake came after a smaller earthquake in Arauco Province at 06:02 on 21 May 1960. Telecommunications to southern Chile were cut off and President Jorge Alessandri had to cancel the traditional ceremony of the Battle of Iquique memorial holiday to oversee the emergency assistance efforts. The government was just beginning to organize help to the affected region when the second earthquake occurred at 14:55 UTC on 22 May in Valdivia.

The second earthquake affected all of Chile between Talca and Chiloé Island, more than 400,000 square kilometers (154,440.9 sq mi). Coastal villages, such as Toltén, disappeared. Later studies argued that the earthquake actually had 37 epicenters through a 1,350 km (839 mi) north-south line that lasted from 22 May to 6 June.^[4] At Corral, the main port of Valdivia, the water level rose 4 m (13 ft) before it began to recede. At 16:20 UTC, an 8 m (26 ft) wave struck the Chilean coast, mainly between Concepción and Chiloe. Ten minutes later, another wave measuring 10 m (33 ft) was reported.

Hundreds of people were already reported dead by the time the tsunami struck. One ship, El Canelo, starting at the mouth of Valdivia River sank after being moved 1.5 km (1 mi) backward and forward in the river. The mast of the Canelo is still visible from the road to Niebla.^[4]

A number of Spanish-colonial fortification were completely destroyed. Soil subsidence also destroyed buildings, deepened local rivers, and created wetlands in places like the Río Cruces and Chorocomayo, a new aquatic park north of the city. Extensive areas of the city were flooded. The electricity and water systems of Valdivia were totally destroyed. Witnesses reported underground water flowing up through the soil. Despite the heavy rains of 21 May, the city was without a water supply. The river turned brown with sediment from landslides and was full of floating debris, including entire houses. The lack of potable water became a serious problem in one of Chile's most rainy regions.

The earthquake did not strike all the territory with the same strength; measured with the Mercalli scale tectonically depressed areas suffered heavier damages. The two most affected areas were Valdivia and Puerto Octay near the northwest corner Llanquihue Lake. The overall picture of damages showed that Puerto Octay was the center of a north-south elliptical area in the Central Valley where the intensity was at its highest if not counting the Valdivia Basin. East of Puerto Octay in a hotel in Todos los Santos Lake piles of plates were reported to have remained in place.

Two days after the earthquake, Cordón Caulle a volcanic vent close to Puyehue volcano erupted. It is possible that other volcanoes also erupted, but none were recorded due to the lack of communication in Chile at that time. The relatively low death toll in Chile (estimated at 6,000) is explained in part by the low population density and the fact that this region is a very active geological zone and builders know they have to build stronger structures. Other possible reasons include a high number of wooden houses and that coastal towns also tended to be located on higher ground, following a pre-Hispanic tradition.^{[citation needed]}

[edit] Tectonic interpretation

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The earthquake was a megathrust earthquake resulting from the release of mechanical stress between the subducting Nazca Plate and the South American Plate. The depth of the focus, 33 km, was relatively shallow considering that earthquakes in northern Chile and Argentina may reach depths of 70 km. Subduction zones are known to produce the strongest earthquakes on earth as their particular structure allows more stress to build up before energy is released. Geophysicists consider it a matter of time before this earthquake will be surpassed in magnitude by another. The earthquake's rupture zone was 800 km long, stretching from Talca (35° S) to Chiloé Archipelago (43° S). The rupture velocity has been estimated as 3.5 km per second.^[5]

[edit] Natural disasters triggered

[edit] Landslides

The earthquake triggered numerous landslides, principally in the step glacial valley of the southern Andes. Within the Andes most landslides occurred in forested mountainsslopes around the Liquiñe-Ofqui Fault. Some of this areas remains with scarce vegetation while other have naturally developed more less pure stands of Nothofagus dombeyi. These landslides did not caused many deaths nor economical losses since the area where most occurred is sparcelly populated with only minor roads. One landslide did however cause several alarm and destruction the one that blocked the outflow of Riñihue Lake (see Riñihuazo).

[edit] Tsunami

Map showing the areas affected by the tsunami.

Earthquake induced tsunamis affected southern Chile, Hawaii, Japan, the Philippines, eastern New Zealand, south east Australia and the Aleutian Islands. Some localised tsunamis severely battered the Chilean coast, with waves up to 25 metres (82 ft). The main tsunami raced across the Pacific Ocean and devastated Hilo, Hawaii. In Hilo, the tsunami claimed 61 lives, allegedly due to people's failure to heed warning sirens. Hilo's position in the bay caused an accumulative bounce of tsunami waves far more destructive to Hilo than to other more exposed areas of Hawaii. Tsunami waves as high as 10.7 metres (35 ft) were recorded 10,000 kilometres (6,000 miles) from the epicentre, and as far away as Japan and the Philippines.

[edit] Riñihuazo flood

During the Great Chilean Earthquake, several landslides west of Tralcán Mountain blocked the outflow of Riñihue Lake (39°45′00″S 72°30′00″W / 39.75°S 72.5°W / -39.75; -72.5). Riñihue Lake is the lowest of the Seven Lakes chain and receives a constant inflow from the Enco River. The blocked San Pedro River, which drains the lake, passes through several towns and the city of Valdivia before finally reaching Corral Bay.

Because the San Pedro River was blocked, the water level of Riñihue Lake started to rise quickly. Each meter the water level rose was equivalent to 20 million cubic meters, which meant that 4800 million cubic meters of water would release into the San Pedro River (easily overpowering its flow capacity of 400 cubic meters (14,126 cubic feet)) if it rose above the final, 24-meter-high dam. This potential disaster would have violently flooded all the settlements along the course of the river in less than five hours, and had more dire consequences if the dam suddenly broke.

About 100,000 people lived in the affected zone. Plans were made to evacuate Valdivia, and many people left. To avoid the destruction of the city, several military units and hundreds of workers from ENDESA, CORFO, and MOP started an effort, called the Riñihuazo, to control the lake. Twenty-seven bulldozers were put into service, but they had severe difficulties moving in the mud near the dams, so dykes had to be constructed with shovels. The work was not restricted to the lake; drainages from other parts of the Seven Lakes were also dammed to minimize the flow into Riñihue Lake. These dams were removed later, with the exception of Calafquén Lake, which still retains its dam.

By 23 June, the main dam had been lowered from 24 m (79 ft) to 15 m (49 ft), allowing 3000 million cubic meters of water to leave the lake gradually, but still with considerable destructive power. The team was led by ENDESA engineer Raúl Sáez.

[edit] Cordón Caulle eruption

Eruption of Cordón Caulle following the 1960 Valdivia earthquake

On May 24, 38 hours after the main shock of the 1960 Valdivia earthquake Cordón Caulle begun a rhyodacitic fissure eruption. Being Cordón Caulle located between two sparsely populated and by then isolated Andean valleys the eruption had few eyewitnesses and received little attention by local media due to huge damages and losses caused by the proper earthquake.^[6] The eruption was fed a 5.5 km long and N135° trending fissure where 21 individual vents have been found. These vents produced an output of about 0.25 km³ DRE both in form of lava flows and tephra. The eruption ended on July 22.

[edit] Consequences and response

[edit] Human sacrifice

A book by investigative journalist Patrick Tierney, The Highest Altar: Unveiling the Mystery of Human Sacrifice (1989) ISBN 9780140139747, documents a possible modern ritual human sacrifice during the devastating earthquake and tsunami of 1960 by a machi of the Mapuche in the Lago Budi community. The victim, 5 year old José Luis Painecur, had his arms and legs removed by Juan Pañán and Juan José Painecur (the victim's grandfather), and was stuck into the sand of the beach like a stake. The waters of the Pacific Ocean then carried the body out to sea. The sacrifice was rumored to be at the behest of local machi, Juana Namuncurá Añen. The 2 men were charged with the crime and confessed, but later recanted. They were released after 2 years. A judge ruled that those involved had "acted without free will, driven by an irresistible natural force of ancestral tradition." The story was mentioned in a Time magazine article, although with little detail.^[7]

[edit] Creation of emergency committee

After the 1960 Valdivia earthquake a committee was formed to solve problems caused by the earthquake. However this committee was not dissolved afterward and in 1974 it became ONEMI (Spanish acronym for National Emergency and Information Office) when it acquired by law independent status as governmental office.

[edit] Urban impact in Valdivia

It has been estimated that about 40% of the houses in Valdivia were destroyed leaving 20,000 people homeless. The most affected structures were those built of concrete that in some cases collapsed completely due to lack of earthquake engineering. Traditional wooden houses fared better and were left in many places uninhabitable but without collapse. Houses built upon tectonically elevated areas suffered considerably less damage comparing to those on the lowlands. Many city blocks with destroyed buildings in the city center remained empty until the 1990s and 2000s being some of them still used as parking lots. Some of this blocks had before the earthquake had modern concrete buildings, those built after the great fire of 1909. In terms of urban development Valdivia suffered the loss of the minor but significant Cau-Cau bridge, a bridge that has not been rebuilt. The other bridges suffered only minor damage. Land subsidence in Corral Bay improved navigability as shoal banks produced by sediments from Madre de Dios and other nearby gold mines sunk and compacted.

The earthquake and the degradation to a provincial capital are seen in retrospect as the culmination of a long period of economic decline that begun with shifts in trade routes due to the expansion of railroad in southern Chile and the opening of Panama Canal in 1911. The industrial activity in Valdivia, dominated by Germans, declined further due to human and capital migration after the earthquake. Several industries such as the Anwandter brewery and the Rudloff shoe factory had their facilities destroyed to the ground and activity was laid down.

In 1974 when the military government of Chile reorganized the countries administrative divisions, Valdivia lost it capital status to Puerto Montt. Valdivia had previously been a first level administrative center since the 16th century and regained its status in 2007 with the creation of Los Ríos Region.

[edit] Previous earthquakes

There is evidence that a similar landslide and earthquake occurred in 1575. ^[8] This earthquake was of similar strength and also caused a Riñihuazo. According to Mariño de Lobera, corregidor of Valdivia by 1575, a landslide blocked the outflow of the lagoon of Renigua and several months later caused a flood. Mariño de Lobera states that while the flood killed a lot of Indians Spanish settlers waited on high ground until the burst of the dam.

[edit] In popular culture

A 1969 episode of the U.S. television series Hawaii Five-O titled 'Forty Feet High And It Kills' referenced the tsunami which devastated Hilo in 1960.

[edit] See also

• 1964 Villarrica eruption
• List of earthquakes in Chile

[edit] References

[edit] External links

• Chilean earthquake and tsunami
• USGS: Chilean earthquake: surviving the tsunamis
• Tsunami of 1960
• Hawaii Events

Coordinates: 38°14′S 73°03′W / 38.24°S 73.05°W / -38.24; -73.05